1. Field of the Invention
The present invention relates to a light quantity control unit used in various camera devices such as video cameras and still cameras. Specifically, it relates to a light quantity control unit such as a diaphragm for regulating the amount of light in a photographing operation or a shutter for blocking the light in a photographing operation and a camera device using the same.
2. Description of the Related Arts
This type of light quantity control unit is comprised of a ring shape base plate integrated in the photographing lens part and has an optical axis aperture, one or a plurality of blade members being revolvingly mounted to this base plate and border on the aperture, and an electro-magnetic drive unit interlocked to the blade member and mounted to said base plate. By applying an electric current to this electro-magnetic drive unit, said blade member revolves and the aperture is blocked or the diameter of the aperture is reduced.
Conventionally, this electro-magnetic drive unit was integrated into one body with said base plate and various methods thereof have been proposed. As a representative drive unit, there is a method of supporting and holding a magnetic rotor with a coil frame revolving freely, winding a coil on the coil frame to envelope the rotor, covering the periphery thereof with a yoke, and revolving the rotor according to Fleming""s left-hand rule by exciting this coil as is disclosed, for example, in Japanese Patent Publication (Kokaihei) No. 10-221740. Even as described in Kokaihei 10-221740, what mounts this drive unit on the aforementioned base plate and transmits the rotating force of said magnet rotor to the blade member is proposed.
Also, there is another method of supporting and holding a magnet rotor at the peripheral part of the base plate in the direction of the optical axis, mounting a coil wound similarly at the peripheral part in the direction orthogonal to the optical axis, opposingly arranging the leading ends of a pair of soft magnetic members engaged at the one ends to said coil at the periphery of said magnet rotor, forming magnetic poles at the leading ends of these soft magnetic members by conducting to the coil, and obtaining a turning torque between the magnetic poles polarized in the magnetic rotor as is proposed, for example, in Japanese Patent Publication (Kokaihei) No. 6-258683. When using this method, a coil, paired soft magnetic members and a magnetic roller are arranged.
The aforementioned prior art has the following demerits. The drive unit in the method disclosed in Kokaihei 10-221740 has a demerit of the drive unit becoming large since there is a coil frame at the periphery of the magnet rotor, a coil at the periphery thereof, and the entire body covered with a yoke. Also, a coil frame exists between the magnet rotor and the coil thus the efficiency degrades due to the thickness thereof. Therefore, it is necessary to increase the number of windings of the coil and the drive unit becomes large. In particular, when arranging plural drive units such as for the shutter blade and for the diaphragm blade at the periphery of the base plate, there is a demerit of causing the drive unit to become large or the opening and closing speed of the blades becoming slow from decreasing the number of windings of the coil.
Next, the drive unit in the method disclosed in Kokaihei 6-258683 has a demerit of the major diameter of the base plate becoming large since the cylindrical coil and the pair of soft magnetic members extended from the two open ends of this coil are arranged at the periphery of the base plate in a horizontal position. This method was particularly difficult to apply when arranging a plurality of drive units at the periphery of the base plate.
An object of the present invention is to provide a light quantity control unit having a compact drive unit of small major diameter, which takes up small space in the direction of the optical axis, at the periphery of the optical axis of the photographing lens part.
Another object of the present invention is to provide a compact light control unit integrated with a plurality of blades such as diaphragm blades and shutter blades and a plurality of drivers.
Still another object of the present invention is to provide a compact camera device integrated with the aforementioned light quantity control unit.
In order to achieve the aforementioned purpose, this invention is composed as follows.
First of all, a blade member having an aperture is arranged on a base plate to border on the aperture. Then, a coil and a magnet rotor of a substantially cylindrical shape are arranged on this base plate at a parallel with a space in-between and with the axial direction thereof oriented in the direction of the optical axis. Then, a pair of magnetic force inducing members are extended from the two end parts of said coil, which are the end parts in the direction of the optical axis, and the leading ends thereof are opposingly arranged with said magnet rotor interposed. Then N pole-S pole are formed in this pair of magnetic force inducing members at the two mutually opposing magnetic poles. Also, N pole-S pole are polarized in said magnet rotor thus the magnet rotor receives a rotating force from the mutual magnetic function of the magnetic poles of the magnetic force inducing members and the magnet rotor. Then, the revolving motion of the magnet rotor is swung at a predetermined angle by a regulating means, which regulates the movement between the two magnetic poles formed in the aforementioned magnetic force inducing members.
By composing the light quantity control unit as described above, the coil and the magnet motor occupy the space in the direction of the optical axis on a base plate normally formed into a ring shape and the magnetic force inducing members occupy the space in the direction orthogonal to the optical axis. Furthermore, rotating force is bestowed to the magnet rotor by the mutual magnetic function of the two polarized magnetic poles and the two magnetic poles formed in the magnetic force inducing members so the structure is simple. As a result, the unit can be miniaturized.
What is more preferable is to engage the base end parts of the aforementioned pair of magnetic force inducing members with the two open ends of the aforementioned coil, bend at least one section at the leading ends of the aforementioned paired magnetic force inducing members, and oppose at approximately the center part in the length wise direction which is the direction of the optical axis of said coil. By doing so, the magnetic resistances of the pair of magnetic force inducing members are equalized, the magnetic field formed in the coil transmits the respective magnetic force inducing member, and both N-S poles of approximately equal magnetic force can be formed at the opposing leading ends.
Note that arranging the leading ends of the magnetic force inducing members at the center position in the length wise direction which is the direction of the optical axis of the coil is most preferable in this case but an appropriate position between the two end parts of the coil, which are the end parts in the direction of the optical axis, should be selected based on the arranged relationship with the other parts.
Furthermore, the aforementioned regulating means can change the speed for opening and closing the blade member(s) by differentiating the attraction force formed between the pair of magnetic force inducing members and the two magnetic poles N-S of the aforementioned magnet rotor between the open area and the close area. Namely, the blades can be closed from the opened state at a high speed by setting the attraction force in the open area to be less than the close area.
It is possible to change the amount of said attraction force by differentiating the shape or the material of the pair of inducing members, which form the magnetic poles. Also, it is possible to change the amount of said attraction force by differentiating the distance of the magnetic poles in the magnet rotor and the magnetic poles in the aforementioned pair of magnetic force inducing members between the open area and the closed area.
To mount the aforementioned coil and the magnet rotor on the aforementioned base plate at a parallel, a holding member is provided to the base plate with a space in-between in the direction of the optical axis and mount the coil and the magnet rotor between this holding member and the base plate so that the two ends thereof are supported by the holding member and the base plate.